1. Field of the Invention
This invention relates to equipment for installing thermowells and similar devices in pipelines and other members and it particularly relates to a method and apparatus for the installation of thermowells, corrosion probes, injection nozzles, sampling taps and the like in pipelines and similar members without taking such members out of service.
2. Background of the Invention
Hot tapping machines are frequently used to permit the cutting of holes in pipes and similar members containing fluids under pressure. Such a machine normally consists of an elongated chamber containing an internal shaft to which a drill can be connected for rotary and longitudinal movement through a packing gland at the upper end of the chamber. The lower end of the chamber is threaded or fitted with a flange so that it can be connected to a fitting which is welded to the surface of a pipe or other member or in some cases clamped around it. This fitting will include a check or gate-type valve which can be opened at the beginning of the hot tapping operation and closed at the conclusion of the operation. This fitting is left in place after the opening in the pipe or other member has been cut. The fitting is quite expensive, generally over $1000 and the necessity to leave it placed has made hot tapping a costly operation.
The installation of a thermowell, test probe or similar device in a pipeline or other member during service normally requires hot tapping of the member as described above and insertion of the thermowell or other device through an elongated packing gland containing a series of packing rings by means of jacking screws. This procedure is time consuming and hazardous in that the packing rings may leak and permit the escape of high pressure fluids during the operation. If the pipe or other member contains flammable gases, a fire or explosion may result. Moreover, the force required to overcome the friction of the packing glands and internal pressure in the system may result in bending or damage to the thermowell or other device, preventing completion of the operation and necessitating shutdown of the system. Furthermore, if the hot tap is no longer needed the entire fitting had to be left in place. As a result of these and related difficulties, conventional methods and equipment for the installation of thermowells and similar devices in pipelines and other vessels containing fluids under pressure leave much to be desired.